Step-down switching regulators are commonly used. The necessity to deliver more current on the same output has generated a multiphase and parallelable class of such switching regulators. A typical multi-phase regulator is shown in FIG. 1. One issue to be solved when paralleling or interleaving is to generate the correct phasing or the equivalent correct time positioning of the switching node SW rise time. As illustrated on FIG. 1, SW1, SW2 and SW3 are precisely positioned in a period so that the distance between the rising edges is T/3 or 120°. In the case of a system with n phases, the distances will be T/n or 360/n.
Some known attempted solutions are generated for fixed frequency DC-DC control systems (e.g., Voltage Mode Control, Peak Current Mode Control, and Average Current Mode Control). The precise phasing information is obtained using the main clock from the master and adding programmable delays in the slaves as shown in FIGS. 2 and 3. FIG. 2 illustrates the circuit diagram for a TPS40140 STACKABLE 2 CHANNEL MULTIPHASE INDEPENDENT OUTPUT CONTROLLER from Texas Instruments, showing a master controller and five slave controllers. FIG. 3 illustrates the circuit diagram for a TPS40180 SINGLE PHASE STACKABLE CONTROLLER from Texas Instruments, showing a single-output stacked configuration of a master controller and three slave controllers.
Other known attempted solutions are the TPS51727 DUAL-PHASE, ECO-MODE™ STEP-DOWN POWER MANAGEMENT IC FOR 50-A+ APPLICATIONS from Texas Instruments. In a steady-state condition, the two phases of the TPS51727 switch 180° out-of-phase. The phase displacement is maintained both by the architecture (which does not allow both top gate drives to be on in any condition) and the current ripple (which forces the pulses to be spaced equally). The TPS51727 is based on current ripple to realize the phasing and regulation and due to the architecture choice cannot work with duty cycles greater than 50%. The ripple in front of the Pulse Width Modulation (PWM) comparator is realized by injecting the measured current ripple. The attempted solution offered by the TPS51727 COT controller does not allow paralleling several chips to realize 4, 6, 8, 10, 12, etc. phase systems, nor are the chips stackable, or parallelable.
Solving the interleaving/phasing issue opens the way to add other necessary features such as current sharing/balancing, adaptive voltage positioning, and phase shedding.
Voltage mode control multiphase and parallelable switching regulators have the advantage of solving the interleaving problem by creating shifted-saw tooth waveforms which, when compared with the error amplifier output, generates correct phased signals. These paralleled switching regulators share the same clock and the information to program the slave for 180 degree for two switchers, 120 degree for three switchers, and 90 degree for four switchers. Also, each switcher needs current sensing and a correction of each duty cycle using the current information to allow balanced current in each phase to allow equal power dissipation. The correct current sharing requires precise current sensing and analog signal processing. This means the generation of the equivalent average current and control of the duty cycle of each phase to get the phase current equal with the average.
Current mode control (average, peak, valley) also has the advantage of solving the interleaving problem by sharing the same clock and generating from that the necessary phase for each switcher. This type of control has the advantage of using the sensed current not only in the control loop but also to obtain precise current sharing through each phase. The necessary added slope compensation in this case presents additional challenges related to precision, trimming and matching for different chips.
A subcategory of the multiphase and parallelable switching regulators is the ripple controlled constant on-time step-down controllers with ripple injection. In particular, constant on-time controllers have a variable frequency resulting from the fact that in order to regulate, TOFF is modulated. The above situation makes the problem of precise interleaving/phasing more difficult. In order to keep the advantages of the fast transient of the Constant TON it also is desirable to have each phase behave independently with respect to modulating its TOFF.
An example of a proposed solution is described in U.S. Pat. No. 9,383,761. In this solution, a “common switching frequency and a common period” are used together with “a clock divider” and “ring of D flip-flops” to generate the interleaving. Another example of a phase interleaving solution is where one TON generator is distributed sequentially to each phase using a multiplexer. While this insures precise identical TON, it denies the possibility of TON time superposition and limits the duty cycle to values greater than 50%.